Composition for detecting alpha particle radiation and methods of use

ABSTRACT

A capsule composition comprising: (a) a polyester shell having a thickness of no more than 20 microns, and (b) a solution containing a visual and/or olfactory indicator, wherein the solution is encapsulated by the polyester shell. Also described herein is a method for detecting alpha particle radiation, in which: (i) the capsule composition is placed in contact with an esterase in a location where the presence of alpha particle radiation is being determined; (ii) waiting a period of time for the esterase to degrade the polyester shells, wherein the period of time is insufficient for the esterase to cause leakage of the solution in the absence of alpha particle radiation but is sufficient for alpha particle radiation, if present, to cause leakage from the capsule composition; and (iii) observing whether leakage has occurred at the end of the period of time to determine whether alpha particle radiation is present.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims benefit of U.S. Provisional ApplicationNo. 62/795,118, filed on Jan. 22, 2019, all of the contents of which areincorporated herein by reference.

GOVERNMENT SUPPORT

This invention was made with government support under Prime Contract No.DE-AC05-00OR22725 awarded by the U.S. Department of Energy. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to methods and devices fordetecting alpha particle radiation and more particularly, tocompositions and methods for visual detection of such radiation.

BACKGROUND OF THE INVENTION

A variety of handheld and laboratory instruments have been developed fordetecting and measuring radiation, including Geiger counters, sodiumiodide detectors, ionization chambers, liquid scintillation counters,and multichannel analyzers. These are generally costly, require complexelectronics, and typically require operators to be in close proximity topotentially hazardous levels of alpha particle radiation for unsafeperiods of time. For the on-site detection of alpha-particle radiation,end window Geiger tubes generally must be held close to the source ofcontamination, and they typically do not distinguish between alpha- andbeta-radiation. Conventional practice is for radiological technicians tosurvey radiological areas by standing close with either handheldinstruments or by obtaining ‘swipes’ of surfaces and conducting analysesof the transferable contamination removed by the swipe. This processforces the technician to interact with potential contamination andincreases the risk to radiation workers and to the facility andenvironment by the possibility of transferring the contamination to evenwider distributions. Thus, there would be a significant advantage in amethod for detecting alpha particle radiation that is low cost, relieson straight-forward sensory observation, and does not require operatorsto be in close proximity to radioactive sources for unsafe periods oftime.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a capsulecomposition containing a visual or olfactory indicator, wherein thecapsules possess the property of leaking the visual or olfactoryindicator only when exposed to alpha particle radiation. The capsuleshave the following composition: (a) a polyester shell having a thicknessof no more than 20 microns, and (b) a solution containing a visual orolfactory indicator, wherein the solution is encapsulated by thepolyester shell. The polyester may be, for example, apolyhydroxyalkanoate, such as polylactic acid, polyglycolic acid,poly(3-hydroxypropionic acid), poly(hydroxybutyric acid)s,poly(hydroxyvaleric acid)s, poly(hydroxyhexanoic acid)s,polycaprolactone, polymandelic acid, or copolymer thereof. The visualindicator may be, for example, a fluorophore or a non-fluorophore dye.The olfactory indicator may be, for example, an amine compound,mercaptan compound, plant-derived scent, perfume, or subtle scentdetectable by sniffer dogs.

In another aspect, the invention is directed to a method for detectingalpha particle radiation using the above described capsule composition.In brief, the method operates by contacting the above described capsulecomposition with an esterase (polyester shell etchant) in a locationwhere alpha particle radiation is suspected, wherein the esterase iscapable of etching the polyester shell, thereby causing its ultimatedegradation and leakage of the internal solution. Alpha particleradiation, if such radiation is present, initiates chemically reactivedefect sites within the polyester shell which facilitates more rapidetching by the esterase. The enhanced etching caused by alpha particleradiation results in leakage of the capsules in much shorter time thanwould be possible by the esterase alone. Thus, by this method, alphaparticle radiation can be determined to be present if leakage of theindicator solution from the capsules is observed to occur in a shortertime period than is known to occur from the esterase alone (i.e., in theabsence of alpha particle radiation) over the same time period.

In some embodiments, the method more particularly includes the followingsteps: (i) placing a capsule composition and an esterase in contact witheach other in a location where the presence of alpha particle radiationis being determined, wherein the capsule composition includes: (a)polyester shells having a thickness of no more than 20 microns, and (b)a solution containing a visual or olfactory indicator, wherein thesolution is encapsulated by the polyester shells; (ii) waiting a periodof time for the esterase to degrade the polyester shells, wherein theperiod of time is insufficient for the esterase to cause leakage of thesolution from the capsule composition in the absence of alpha particleradiation, while the same period of time is sufficient for alphaparticle radiation, if present, to facilitate degradation of thepolyester shells to the extent that leakage from the capsule compositionwould occur; and (iii) observing whether leakage from the capsulecomposition occurs at the completion of the period of time to determinewhether alpha particle radiation is present.

In further embodiments, the method more particularly includes thefollowing steps: (i) placing the above-described capsule composition andan esterase in contact with each other in a location where the presenceof alpha particle radiation is being determined, wherein the capsulecomposition includes: (a) polyester shells having a thickness of no morethan 20 microns, and (b) a solution containing a visual or olfactoryindicator, wherein the solution is encapsulated by the polyester shells;(ii) waiting a period of time for the esterase to initiate low-leveldefects in the polyester shells without causing leakage of the capsulecomposition, and waiting a further period of time during which theesterase is incapable of etching the polyester shells to the extent thatleakage from the capsule composition would occur, while the furtherperiod of time is also sufficient for alpha particle radiation, ifpresent, to etch the polyester shells to the extent that leakage fromthe capsule composition would occur; and (iii) observing whether leakagefrom the capsule composition occurs at the completion of the furtherperiod of time to determine whether alpha particle radiation is present.

In other embodiments, the method more particularly includes thefollowing steps: (i) placing the above-described capsule composition andan esterase in contact with each other in a location where the presenceof alpha particle radiation is being determined, wherein the capsulecomposition comprises: (a) polyester shells having a thickness of nomore than 20 microns, and (b) a solution containing a visual orolfactory indicator, wherein the solution is encapsulated by thepolyester shells; (ii) waiting a period of time for the esterase todegrade the polyester shells to an extent that the solution within thecapsules leaks out of at least a portion of the capsules; (iii)detecting the leaked visual or olfactory indicator to determine theextent of leakage of the solution; and (iv) comparing the extent ofleakage in step (iii) with the extent of leakage in a control experimentunder the same conditions except that alpha particle radiation is knownnot to be present, wherein, if the extent of leakage observed in step(iii) is determined to be greater than the extent of leakage of thecontrol, alpha particle radiation is determined to be present.

The above described methods advantageously permit crews to preciselylocate sources of alpha radiation contamination within a facility in asafe and straight-forward manner. In some embodiments, the abovedescribed method is practiced by deploying a biodegradable aerosolizedindicator system containing the capsule composition and esterase(etchant). In other embodiments, the above described method is practicedby placing (e.g., affixing) the capsule composition and esterase etchanton a sheet substrate material when placed in a location where thepresence of alpha particle radiation is being determined. The abovedescribed approach advantageously relies on polymeric, biodegradablecapsules filled with visual (e.g., fluorescent or dye) or olfactoryindicators that can be enzymatically released over short time periodsunder dry, ambient air laboratory conditions, and this release isenhanced by exposure of these capsules to alpha particle radiation. Thissystem provides a novel means of safely and accurately visualizing theprecise locations of alpha contamination within a facility, providingsafer, faster, and more effective planning and execution ofdecontamination operations.

In some embodiments, the above described method is particularly directedto the detection of radon. In embodiments where the presence of radon isbeing tested, the method may further include, before step (i), placingan absorbent material that absorbs radon yet does not block alphaparticle emission in a location where the presence of radon is beingdetermined, and, in step (i), placing the capsule composition andesterase in contact with each other on the absorbent material after theabsorbent material is provided sufficient time to absorb radon. In moreparticular embodiments, the method may further include, before step (i),placing an absorbent material that absorbs radon yet does not blockalpha particle emission on selective portions of a substrate to resultin regions of the substrate containing the absorbent material andregions of the substrate not containing the absorbent material, andplacing the substrate in a location where the presence of radon is beingdetermined, and, in step (i), placing the capsule composition andesterase in contact with each other on the regions containing theabsorbent material and the regions not containing the absorbent materialafter the absorbent material is provided sufficient time to absorbradon; proceeding with step (ii); and in step (iii), determining thepresence of (or extent of) leakage of the solution in regions containingthe absorbent material and comparing this result to regions notcontaining the absorbent material to determine if regions containing theabsorbent material exhibit leakage (or a higher leakage) of the solutioncompared to regions not containing the absorbent material. In particularembodiments, the absorbent material is or includes a cryptophanematerial.

In the above described method for detection of radon, the alpharadiation emitted by the radon captured within the absorbent layer willemit in all directions. Thus, in some embodiments, the radon absorbentmaterial is sandwiched between layers of the capsule composition tomaximize interaction of radon alpha particle radiation with thecapsules, thereby resulting in an improved measurement sensitivity ofthe device. Further, all radon daughter products will remain capturedwithin the sandwiched layer, and their alpha emissions will also beforced to interact with the indicating capsule layer. Ideally, the topand bottom capsule layers should be of a thickness such that each alphaemission travels through multiple capsules, thereby promoting therelease of measurable amounts of capsule fill material. For example,with PLGA microcapsules that are 300 nm in diameter, a 20 micron-thickcapsule layer would provide alpha traversal of approximately 60-70capsules for alpha emissions oriented perpendicular to the planarsurface of the detector.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plot showing release of fluorescent dye from PLGAmicrocapsules exposed over extended time periods to lipase derived fromRhizopus oryzae, potassium phosphate buffer at pH 8.0, and Tween® 20.Microcapsules and enzyme mixture was co-deposited upon Durx® 770 fabricand incubated at temperatures of 20-23° C. at relative humidity ofapproximately 40%.

FIG. 2 is a photograph showing dye release from PLGA capsulesimmobilized onto Durx® 770 clean room wipes and maintained under dry (RH40%) laboratory conditions (20-23° C.). At top, the capsules were notexposed to enzyme degradation, resulting in negligible leakage.Capsules/enzymes were a mixture of capsules, enzymes, buffer, andsurfactant and resulted in measurable leakage within 15 hours. Enzymealone produced fluorescence, but at a different spectral characteristicwhich can be discriminated from the fluorophore contained within thecapsules.

FIG. 3 is a graph plotting rewetted fluorescence vs. exposure time ofcapsules/lipase/potassium phosphate/and surfactance immobilized ontoDurx® 770 clean room wipes and maintained under dry (RH 40%) laboratoryconditions (20-23° C.) following timed exposures to alpha particles froma 0.9 microCurie americium-241 source. The graph shows that alphaparticle exposure enhances the enzymatic leakage of fluorescein dye fromPLGA capsules. Capsules were exposed to alpha particle radiation from anAm-241 source for various lengths of time, and capsules weresubsequently enzymatically degraded under dry (40% RH) laboratoryconditions (20-23° C.). Amount of dye leakage was determined at 72 hoursand correlates with the amount of alpha exposure experienced by thecapsules.

FIG. 4 is a bar chart showing the fluorescence of intact (contained) andruptured (released) PLGA microcapsules formulated with various internalfluorescent solutions including 4 mM sodium fluorescein, emulsifiedsodium fluorescein within mineral oil, 100 mM sodium fluorescein, andFAM-labelled peptide nucleic acid. In each case, the internalfluorescent solution is not indicated until the microcapsule is degradedby exposure to potassium hydroxide. This demonstrates that intactcapsules effectively prevent visualization of fluorescence and thatvarious fluorescent indicators can be used.

FIG. 5 is a bar chart showing the observed fluorescence of PLGAmicrocapsules filled with a sodium fluorescein solution after iterativeexposure to various solvents. Four spots of microcapsules were depositedfrom a liquid suspension and dried on Durx® 770 clean room wipes andtheir fluorescence emission was determined (initial drydown). Each spotwas then rewetted with ethanol and fluorescence remeasured (threetimes). Each spot was then rewetted with methanol and fluorescenceremeasured (three times). Finally, each spot was degraded with potassiumhydroxide which released the internal dye solution and caused markedincrease in visual fluorescence.

FIG. 6 is a line chart of the fluorescence emission from PLGAmicrocapsules containing sodium fluorescein over time when colocalizedwith potassium phosphate buffer (pH 8.0) triton x-100 and variousamounts of lipase enzyme. Increasing the amount of lipase results infaster degradation and fluorescence release from microcapsules. Heatdenaturation of the enzyme diminishes the enzymes ability to degrade andrelease fluorescence from the microcapsules.

FIGS. 7A and 7B are bar charts which demonstrate that differentformulations of PLGA result in differing characteristics with respect toenzymatic etching and the impact of alpha particle exposure prior toetching. Microcapsules containing sodium fluorescein were co-localizedwith (E+) and without (E−) enzyme, and with (I+) and without (I−) 2minutes of alpha particle exposure 1 cm from a 0.9 microCurie Am-241source. Resomer RG503 microcapsules (FIG. 7A) have some level of leakagewithout enzyme exposure. Enzyme exposure increases the leakage andirradiation further increases this leakage. Lactel B6010 microcapsules(FIG. 7B) provide a larger difference when irradiated, whereby theirradiation appears to enhance enzymatic degradation of themicrocapsule.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect, the present disclosure is directed to a capsulecomposition containing at least or solely the following components: (a)a polyester shell, and (b) a solution containing a visual or olfactoryindicator (i.e., indicator solution), wherein the indicator solution isencapsulated by the polyester shell. For purposes of the presentinvention, the polyester shell preferably has a thickness of no morethan 20 microns, in order to ensure penetration of the alpha particleradiation through the entire shell thickness. Nevertheless, thepolyester shell should be of sufficient thickness to retain theindicator solution prior to being etched by enzyme. In differentembodiments, the polyester shell has a thickness of precisely, about, orless than, for example, 20, 18, 15, 12, 10, 8, 5, 2, 1 micron, or 50nanometers, or a thickness within a range bounded by any two of theforegoing values (e.g., 50 nanometers-20 microns or 50 nanometers-18microns, or 50 nanometers-15 microns).

The polyester shell is composed completely of or includes (e.g., assegments or in admixture) at least one polyester polymer containingester (—C(O)O—) linkages at least in a backbone of the polyesterpolymer. The polyester polymer may or may not also have ester groups inpendant portions or terminal positions of the polymer. The polyesterpolymer can have any of a variety of possible number-average orweight-average molecular weights (M_(n) or M_(w), respectively). Indifferent embodiments, the polyester polymer has a molecular weight ofabout, at least, greater than, up to, or less than, for example, 1,000g/mol, 2,000 g/mol, 5,000 g/mol, 10,000 g/mol, 20,000 g/mol, 30,000g/mol, 40,000 g/mol, 50,000 g/mol, 75,000 g/mol, 100,000 g/mol, 150,000g/mol, 200,000 g/mol, 300,000 g/mol, 500,000 g/mol, or 1,000,000 g/mol,or a molecular weight within a range bounded by any two of the foregoingexemplary values.

In some embodiments, the polyester is a polyhydroxyalkanoate, whichcorresponds to the following generic structure:

In Formula (1), R¹ is selected from a hydrogen atom (H) or hydrocarbongroup (R). The hydrocarbon group (R) can be any saturated or unsaturatedhydrocarbon group, typically containing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, or 12 carbon atoms or a number of carbon atoms within a rangebounded by any two of the foregoing values (e.g., 1-12, 2-12, 3-12, 1-6,1-4, or 1-3 carbon atoms). The hydrocarbon group (R) may be, forexample, a straight-chained (linear) or branched alkyl or alkenyl group,or saturated or unsaturated cyclic hydrocarbon group. In someembodiments, the hydrocarbon group (R) is an alkyl group having one,two, three, four, five, or six carbon atoms, such as a methyl, ethyl,n-propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, isopentyl,cyclopentyl, n-hexyl, isohexyl, or cyclohexyl group. The hydrocarbongroup may, in some cases, be an unsaturated ring, such as a phenylgroup. The hydrocarbon group may also be composed solely of carbon andhydrogen atoms, or may contain one or more heteroatoms selected fromoxygen, nitrogen, and halogen atoms. Thus, in the case of cyclichydrocarbon groups, the cyclic group may be a carbocyclic group or aheterocyclic group. The variable t is typically an integer from 0 to 4.The subscript t is more typically an integer from 0 to 3 (i.e., t istypically 0, 1, 2, or 3). The variable n is typically an integer of atleast 10. In different embodiments, the subscript n is an integer of atleast or greater than 10, 20, 50, 100, 200, 500, 1000, 1500, 2000, 2500,or 5000, or a value within a range bounded therein, or n can be a valuethat results in any of the exemplary molecular weights provided above.In some embodiments, any of the above classes or specific types ofpolyesters may be excluded from the polyester shell.

When t is 0, Formula (1) depicts a polymer of an alpha-hydroxy(α-hydroxy) acid. An example of an α-hydroxy polymer when R¹ in Formula(1) is H is polyglycolic acid. An example of an α-hydroxy polymer whenR¹ is methyl is polylactic acid (i.e., PLA, polymer of2-hydroxypropionic acid, also known as poly-L-lactic acid, poly-D-lacticacid, or poly-DL-lactic acid). An example of an α-hydroxy polymer whenR¹ is phenyl is polymandelic acid. When t is 1, Formula (1) depicts apolymer of a beta-hydroxy (β-hydroxy) acid. An example of a β-hydroxypolymer when R¹ is H is poly(3-hydroxypropionic acid). An example of aβ-hydroxy polymer when R¹ is methyl is poly(3-hydroxybutyric acid)(i.e., P3HB). An example of a β-hydroxy polymer when R¹ is ethyl ispoly(3-hydroxyvaleric acid) (i.e., PHV). An example of a β-hydroxypolymer when R¹ is n-propyl is poly(3-hydroxyhexanoic acid) (i.e., PHH).When t is 2, Formula (1) depicts a polymer of a gamma-hydroxy(γ-hydroxy) acid. An example of a γ-hydroxy polymer when R¹ is H ispoly(4-hydroxybutyric acid) (i.e., P4HB). An example of a γ-hydroxypolymer when R¹ is methyl is poly(4-hydroxyvaleric acid). Some examplesof polyhydroxyalkanoates with t=3 include poly(5-hydroxyvaleric acid)and poly(5-hydroxyhexanoic acid). An example of a polyhydroxyalkanoatewith t=4 includes poly(6-hydroxyhexanoic acid), also known aspolycaprolactone (PCL). In some cases, the polyhydroxyalkanoate may beselected from poly(hydroxypropionic acid)s, poly(hydroxybutyric acid)s,poly(hydroxyvaleric acid)s, or poly(hydroxyhexanoic acid)s. The hydroxyacid need not be within the scope of Formula (1) to be suitable. Forexample, a polymer of salicylic acid may or may not also be considered.In some embodiments, any of the above classes or specific types ofpolyesters may be excluded from the polyester shell.

Copolymers of the hydroxy acids are also considered herein. In someembodiments, two or more different types of hydroxyalkanoates are in thecopolymer, such as in (poly(lactic-co-glycolic acid) (i.e., PLGA),poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (i.e., PHBV), orpoly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In other embodiments, thecopolymer includes one or more non-hydroxyalkanoate portions, as inpoly(glycolide-co-trimethylene carbonate) andpoly(lactide-co-polyethylene glycol). In the case of a PLGA copolymer,the lactic acid (LA) and glycolic acid (GA) units in the PLGA copolymermay, in some embodiments, be independently present in a molar amount of40-60%, wherein the molar amounts of lactic acid and glycolic acid unitssum to 100%. The LA:GA molar ratio may be precisely or about, forexample, 5:95, 10:90, 20:80, 30:70, 40:60, 45:55, 50:50, 55:45, or60:40, or within a range between any two of the foregoing ratios. Insome embodiments, any of the above classes or specific types ofpolyesters may be excluded from the polyester shell.

In some embodiments, the polyester is a diol-diacid type of polyester,i.e., a polyester resulting from the condensation of a diol with adiacid. The diol-diacid types of polyesters can be defined by thefollowing generic structure:

In the above Formula (2), R² and R³ are independently selected fromhydrocarbon linking groups, which can be derived from hydrocarbon groups(R) containing 1-12 carbon atoms, as defined above, by replacing anotherhydrogen atom of the hydrocarbon group with a bond. For example, amethyl (—CH₃) group, selected from R groups, can have a hydrogen atomremoved to result in a methylene (—CH₂—) linking group corresponding toR² and/or R³. The variable n is as described above. In some embodiments,one or both (or at least one) of the linking groups R² and R³ areindependently selected from alkylene groups, i.e., linking groups of theformula —(CH₂)_(n)—, where m is typically 1-12. In other embodiments,one or both (or at least one) of the linking groups R² and R³ areindependently selected from saturated or unsaturated carbocyclic orheterocyclic groups (e.g., cyclopentyl, cyclohexyl, phenylene, and furangroups). In a first set of particular embodiments, R² is phenylene andR³ is an alkylene group, in which case the polyester can be generallyclassified as a polyalkylene terephthalate. In the case where R² isphenylene and R³ is methylene (—CH₂—), the polyester is a polymethyleneterephthalate (PMT); in the case where R² is phenylene and R³ isethylene (—CH₂CH₂—), the polyester is a polyethylene terephthalate(PET); in the case where R² is phenylene and R³ is propylene(—CH₂CH₂CH₂—), the polyester is a polypropylene terephthalate (PPT); inthe case where R² is phenylene and R³ is butylene (—CH₂CH₂CH₂CH₂—), thepolyester is a polybutylene terephthalate (PBT). In a second set ofparticular embodiments, R² and R³ are independently selected fromalkylene groups. In the particular case where R² is ethylene, thepolyester of Formula (2) is herein referred to as a succinate-basedpolyester, e.g., a polyethylene succinate, when R³ is also ethylene; ora polypropylene succinate, when R³ is propylene; or a polybutylenesuccinate, when R³ is butylene. In the particular case where R² isbutylene, the polyester of Formula (2) is herein referred to as anadipate-based polyester, e.g., a polyethylene adipate, when R³ isethylene; or a polypropylene adipate, when R³ is propylene; or apolybutylene adipate, when R³ is also butylene. In some embodiments, R²in Formula (2) may be a bond, which results in oxalate-based polyesters,such as polyethylene oxalates, when R³ is ethylene. Other less common ormore specialized polyesters according to Formula (2) are consideredherein, such as when R² is naphthyl, which corresponds to thenaphthalate-based polyesters, such as polyethylene naphthalate (PEN),when R³ is ethylene, or polybutylene naphthalate (PBN), when R³ isbutylene. In some embodiments, any of the above classes or specifictypes of polyesters may be excluded from the polyester shell.

The polyester may alternatively be any of the vinyl ester andunsaturated polyester resins well known in the art. Vinyl ester resinsare described, for example, in S. Jaswal et al., Reviews in ChemicalEngineering, 30(6), 567-581 (2014); H. M. Kang et al., Journal ofApplied Polymer Science, 79:1042-1053 (2001); and M. A. F. Robertson etal., J. Adhesion, 71:395-416 (1999), the contents of which are hereinincorporated by reference in their entirety. Unsaturated polyesterresins are described in, for example, H. Yang et al., Applied Polymer,79(7), 1230-1242, 2001; M. Malik et al., J. Macromol. Sci. Rev.Macromol. Chem. Phys., C40(2&3), 139-165 (2000); and M. Olesky et al.,Ind. Eng. Chem. Res., 52(20), 6713-6721 (2013), the contents of whichare herein incorporated by reference in their entirety. In someembodiments, any of the above classes or specific types of polyestersmay be excluded from the polyester shell.

The polyester can be terminated by any of the functional groups known inthe art. In some embodiments, the polyester is acid-terminated (i.e.,terminated with one or two carboxylic acid groups). In otherembodiments, the polyester is ester-terminated (i.e., terminated withone or two carboxylic acid ester groups). In other embodiments, thepolyester is hydroxy-terminated. In yet other embodiments, the polyesteris amine-terminated or amide-terminated. The polyester may also have acombination of terminating groups, e.g., ester and hydroxy, orcarboxylic acid and hydroxy.

The visual indicator can be any one or more substances that can bevisually observed directly or indirectly when leaked from the capsulecomposition. Direct visualization is herein understood to meanvisualization of the indicator with the eye of an observer, without anintermediary device to make the indicator visible. Indirectvisualization is herein understood to mean visualization of theindicator by means of an intermediary device (e.g., a laser orwavelength detection or imaging device, or both) to make the indicatorvisible to the eye of the observer. Although in many embodiments thevisual indicator is inherently visible the moment it becomes leaked, insome embodiments, the visual indicator may only become visible byreacting with another component after leaking, e.g., air or a secondchemical contacted with a first leaked chemical.

In some embodiments, the visual indicator is a fluorophore. Thefluorophore may absorb and emit light of any suitable wavelengths. Insome embodiments, it may be desired to select a fluorophore withparticular absorption and emission characteristics. For example, indifferent embodiments, the fluorophore absorbs at nanometer (nm)wavelengths of 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400,420, 440, 460, 480, 500, 520, 540, 560, 580, 600, 620, 640, 660, 680,700, 720, 740, 760, 780, or 800 nm, or a wavelength within a rangebounded by any two of the foregoing values. In different embodiments,the fluorophore emits at any of the foregoing wavelengths, or within arange bounded by any two of the foregoing values, wherein it isunderstood that a fluorophore generally emits at a longer wavelengththan the absorbed wavelength. The impinging electromagnetic radiation(i.e., which is absorbed by the fluorophore) can be in a dispersed form,or alternatively, in a focused form, such as a laser. Moreover, theabsorbed or emitted radiation can be in the form of, for example, farinfrared, infrared, far red, visible, near-ultraviolet, or ultraviolet.

In a first set of embodiments, the fluorophore is an organic molecule,which generally contains at least one carbon-carbon bond and at leastone carbon-hydrogen bond. In different embodiments, the organicfluorophore can include, for example, a charged (i.e., ionic) molecule(e.g., sulfonate or ammonium groups), uncharged (i.e., neutral)molecule, saturated molecule, unsaturated molecule, cyclic molecule,bicyclic molecule, tricyclic molecule, polycyclic molecule, acyclicmolecule, aromatic molecule, and/or heterocyclic molecule (i.e., bybeing ring-substituted by one or more heteroatoms selected from, forexample, nitrogen, oxygen and sulfur). In the particular case ofunsaturated fluorophores, the fluorophore may contain one, two, three,or more carbon-carbon and/or carbon-nitrogen double and/or triple bonds.In some embodiments, the fluorophore contains at least two (e.g., two,three, four, five, or more) conjugated double bonds (i.e., a polyenelinker) aside from any aromatic group that may be in the fluorophore. Inother embodiments, the fluorophore is a fused polycyclic aromatichydrocarbon (PAH) containing at least two, three, four, five, or sixrings (e.g., naphthalene, pyrene, anthracene, chrysene, triphenylene,tetracene, azulene, and phenanthrene) wherein the PAH can be optionallyring-substituted or derivatized by one, two, three or more heteroatoms.The fluorophore may be, for example, a xanthene derivative (e.g.,fluorescein, rhodamine, Oregon green, eosin, or Texas Red), cyanine orits derivatives or subclasses (e.g., streptocyanines, hemicyanines,closed chain cyanines, phycocyanins, allophycocyanins,indocarbocyanines, oxacarbocyanines, thiacarbocyanines, merocyanins, andphthalocyanines), a naphthalene derivative (e.g., dansyl and prodanderivatives), a coumarin or derivative thereof, an oxadiazole orderivative thereof (e.g., pyridyloxazoles, nitrobenzoxadiazoles, andbenzoxadiazoles), a pyrene or derivative thereof, an oxazine orderivative thereof (e.g., Nile Red, Nile Blue, and cresyl violet), anacridine (e.g., proflavin, acridine orange, and acridine yellow), anarylmethine (e.g., auramine, crystal violet, and malachite green), ortetrapyrrole (e.g., porphyrins and bilirubins).

In some embodiments, the fluorophore may be a cyanine dye (i.e.,cyanine-based fluorophore). The term “cyanine dye”, as used herein,refers to any of the dyes, known in the art, that include two indolyl orbenzoxazole ring systems interconnected by a conjugated polyene linker.The cyanine dye typically contains at least two or three conjugatedcarbon-carbon double bonds, at least one of which is not in a ring, suchas depicted in any of Formulas (1)-(3). The cyanine dye (or other typeof dye) often contains at least two pyrrolyl rings. Some particularexamples of cyanine dyes are the Cy® family of dyes, which include, forexample, Cy2, Cy3, Cy3B, Cy3.5, Cy5, Cy5.5, Cy7, and Cy9. The term“cyanine moiety”, as used herein, generally includes thebis-indolyl-polyene or bis-benzoxazolyl-polyene system, but excludesgroups attached to the ring nitrogen atoms in the indolyl orbenzoxazolyl groups. The cyanine dyes may also include the Alexa® familyof dyes (e.g., Alexa Fluor 350, 405, 430, 488, 500, 514, 532, 546, 555,568, 594, 610, 633, 647, 660, 680, 700, 750, and 790), the ATTO® familyof dyes (e.g., ATTO 390, 425, 465, 488, 495, 520, 532, 550, 565, 590,594, 601, 615, 619, 629, 635, 645, 663, 680, 700, 729, and 740), and theDy® family of dyes (e.g., DY 530, 547, 548, 549, 550, 554, 556, 560,590, 610, 615, 630, 631, 631, 632, 633, 634, 635, 636, 647, 648, 649,650, 651, 652, 675, 676, 677, 680, 681, 682, 700, 701, 730, 731, 732,734, 750, 751, 752, 776, 780, 781, 782, and 831). The ATTO dyes, inparticular, can have several structural motifs, including,coumarin-based, rhodamine-based, carbopyronin-based, and oxazine-basedstructural motifs.

The fluorophore may alternatively be an inorganic fluorophore, such as ametal, metal oxide, or quantum dot nanoparticle or microparticle capableof fluorescing when stimulated. The fluorescing ability may be an innateproperty arising from the composition of the particle, or thefluorescing ability may arise from fluorophore doping or surfaceconjugation to an organic fluorophore species. The fluorescent dopantmay be, for example, a lanthanide ion, such as, Ce, Er, Gd, Dy, or Yb.Some examples of metal particle fluorophores include gold and silverparticles. Some examples of metal oxide fluorescent particles includefluorophore-doped silica, titania, or zirconia particles. Some examplesof quantum dot nanoparticles include particles having a zinc sulfide,zinc selenide, zinc telluride, cadmium sulfide, cadmium selenide, orcadmium telluride composition. A detailed description of fluorescentnanoparticles is provided in S. M. Ng et al., RSC Adv., 6, 21624-21661,2016, which is herein incorporated by reference in its entirety.

In another embodiment, the visual indicator is a non-fluorophore dye.Some examples of non-fluorophore dyes include food colorants, azo dyes(e.g., Trypan Blue, Methyl Orange, FD&C Red 40, and FD&C Yellow 5),triphenylmethanes (e.g., Coomassie Blue and Bromocresol Green),Methylene Blue, Neutral Red, and Nile Blue. The term “non-fluorophoredye” herein refers to dyes that do not require electromagneticstimulation to be visualized, i.e., the non-fluorophore dye has a colorthat can be visually observed directly with the eye. In some cases, thenon-fluorophore dye may also possess a fluorescing property, which maybe useful in further detecting the dye, in addition to being directlyvisually observable. Similarly, a fluorophore, such as any of thefluorophores described above, may also in some embodiments be directlyvisually observable, in addition to being indirectly observable byelectromagnetic stimulation.

The olfactory indicator can be any compound or mixture of compounds thatcan be detected by humans, olfactory-acute animals, or electronic (i.e.,artificial) olfactory sensing device. In embodiments where the olfactoryindicator is intended to be detectable by a person, the olfactoryindicator is selected to have a scent much stronger than required fordetection by an olfactory-acute animal or electronic sensing device. Theolfactory indicator may be or include, for example, an amine, thiol,ester (i.e., linear or lactone), ketone, terpene-containing compound, oraromatic compound. In some embodiments, the olfactory indicator may be aperfume (e.g., floral scent) or aromatic spice extract.

The visual or olfactory indicator is typically dissolved or suspended ina solvent, thereby resulting in a solution or suspension of the visualor olfactory indicator. The solvent can be any single solvent or mixtureof solvents that suitably dissolve or suspend the visual or olfactoryindicator while also not being in any way reactive with the polyestershell. The solvent may be or include, for example, aqueous-based (e.g.,water or water admixed with a water-soluble co-solvent), alcohol (e.g.,methanol, ethanol, n-propanol, isopropanol, n-butanol, or ethyleneglycol), nitrile (e.g., acetonitrile or propionitrile), or hydrocarbon(e.g., hexanes, paraffins, or mineral oil). Typically, a solvent thatfully dissolves the visual or olfactory indicator is used. In somecases, the visual or olfactory indicator may itself be a liquid, inwhich case the visual or olfactory indicator may be encapsulated by thepolyester shell by itself, i.e., not as a solution.

In another aspect, the present disclosure is directed to a method forpreparing the capsule composition described above. Any liquidencapsulation method suited to producing capsules of liquid encapsulatedby polyester shells may be used herein. The process may be, for example,an interfacial polymerization, in situ polymerization, coacervation, oremulsion process. In particular embodiments, the method includes a dual(double) emulsion process wherein an amount of a polyester, such as anyof those described above, are dissolved in a solvent and homogenizedwith an indicator solution by ultrasound (e.g., an ultrasonic horn). Theresultant emulsion may then be vortexed in one or more other solutions,followed by ultrasonic homogenization.

In another aspect, the present disclosure is directed to a method fordetecting alpha particle radiation by use of the above-described capsulecomposition. In the method, an esterase is contacted with the capsulecomposition in a location of interest where presence of alpha particleradiation is being determined. The foregoing step of placing the capsulecomposition and esterase in a location of interest is herein referred toas “step (i)”. The esterase functions as an initial etchant of thepolyester shell to result in initial damage sites in the polyestershell, without causing leakage from the capsules. Alpha particleradiation, if present, will cause much quicker and more significantetching at the initial damage sites to the extent that leakage of theindicator solution will occur. Thus, alpha particle radiation can bedetermined to be present if leakage of the indicator solution from thecapsules is observed to occur in a shorter time period than is known tooccur from the esterase alone (i.e., in the absence of alpha particleradiation) over the same time period. The alpha emitting species may beany one or more radioactive elements, typically having an atomic numberat or above 83, that emit alpha radiation, all of which are well knownin the art. The alpha emitting species may be one or more alpha emittingisotopes of, for example, bismuth, polonium, radon, actinium, radium,americium, uranium, thorium, and plutonium.

The esterase can be any of the esterases known in the art, provided thatthe esterase is able to etch the polyester shell material. In particularembodiments, the esterase is a lipase. The esterase is typicallycontacted with the capsule composition in the further presence of abuffer and/or surfactant and/or a humectant. The buffer can be any ofthe pH buffering salts known in the art that can maintain a pH withinwhich the esterase is active, of about 6-8, e.g., Tris buffer, HEPESbuffer, or monobasic/dibasic phosphate buffer. The surfactant can be anyof the amphiphilic molecules or polymers known in the art havinglipophilic and hydrophilic portions, e.g., Triton™ X-100 or thepolyoxyethylenesorbitans, such as polyethylene glycol sorbitanmonolaurate (Tween® 20 or Polysorbate 20). The humectant may be anymaterial which maintains some water activity around the enzyme and themicrocapsule and may include for example polyvinylpyrrolidone, propyleneglycol, glyceryl triacetate, honey, molasses, polydextrose, and sugaralcohols.

In a first set of embodiments, the method more particularly includes thefollowing steps: (i) placing a capsule composition, as described above,and an esterase in contact with each other in a location where thepresence of alpha particle radiation is being determined; (ii) waiting aperiod of time for the esterase to degrade the polyester shells, whereinthe period of time is insufficient for the esterase to cause leakage ofthe solution from the capsule composition in the absence of alphaparticle radiation, while the same period of time is sufficient foralpha particle radiation, if present, to degrade the polyester shells tothe extent that leakage from the capsule composition would occur; and(iii) observing whether leakage from the capsule composition occurs atthe completion of the period of time to determine whether alpha particleradiation is present. The period of time in which the esterase initiallydegrades the polyester shells without causing leakage of the capsulescan be determined by a control experiment in which the esterase iscontacted with the capsules in the absence of alpha particle radiationunder the same conditions in which the testing of presence of alphaparticle radiation is being conducted. The “same conditions” includes atleast the same temperature, the same capsule and esterase compositions,same buffers and surfactants, and same ratio of esterase relative tocapsule composition.

By the control experiment, the operator is aware of the period of timein which the esterase cannot cause leakage of the capsules on its own,i.e., in the absence of alpha particle radiation. In some embodiments,the esterase may, on its own, cause leakage of the capsules if presentin sufficient amount and if given a sufficient period of time for theesterase to cause such degradation. Whether the esterase may, on itsown, eventually cause leakage, can again be determined by a controlexperiment, and the operator is thus aware of the available period oftime until the esterase can cause leakage on its own. In any event, todetermine whether alpha particle radiation is present, the capsules incontact with esterase should be present in the location being tested fora period of time in which the esterase cannot cause leakage on its own.Thus, if leakage occurs at the completion of the period of time of theexperiment, it can be deduced that alpha particle radiation is present.Moreover, in the event alpha particle radiation is determined to bepresent, the amount (magnitude) of alpha particle radiation may also beestimated by observation (which may include calculation) of the amountof leakage. To estimate the amount of alpha particle radiation, furthercontrols can be conducted in which known levels of alpha particleradiation are tested on the capsules in contact with esterase todetermine the levels of leakage resulting from the different levels ofalpha particle radiation.

In other embodiments, the capsules (while in contact with the esterase)are placed in a location where the presence of alpha particle radiationis being determined for a period of time for the esterase to degrade thepolyester shells to an extent that the solution within the capsulesleaks out of at least a portion of the capsules. A subsequent step (stepiii) involves detecting the leaked visual or olfactory indicator todetermine the extent of leakage of the solution. A subsequent step (stepiv) involves comparing the extent of leakage in step (iii) with theextent of leakage in a control experiment under the same conditionsexcept that alpha particle radiation is known not to be present,wherein, if the extent of leakage observed in step (iii) is determinedto be greater than the extent of leakage of the control, alpha particleradiation is determined to be present.

As discussed for any of the exemplary detection methods described above,an esterase is placed in contact with the capsule composition in alocation where the presence of alpha particle radiation is beingdetermined. The capsule composition can be contacted with the esteraseby any suitable means. In one exemplary embodiment, the capsulecomposition and esterase are deposited on a surface in a location beingtested by spraying droplets (e.g., a mist or fog) of both componentsonto the surface. In one embodiment, the two components are sprayedtogether (simultaneously). In another embodiment, the two components aresprayed separately (i.e., as separate sprays), which may be asimultaneous or successive spraying of the two sprays. In anotherexemplary embodiment, the capsule composition and esterase are firstdeposited on a sheet substrate material (e.g., paper, glass, ceramic, ormetal) to produce a testing strip or sheet, and the testing strip orsheet is placed in a location where the presence of alpha particleradiation is being determined. The capsule composition and esterase canbe deposited on the sheet substrate material by any suitable means(e.g., spray coating or dipping followed by drying), provided that themeans for doing so does not interfere with the ability of the capsulesto be etched by the esterase and alpha particle radiation.

In some embodiments, to more precisely determine whether leakage is aresult of the presence of an alpha radiation emitter, an alpha radiationblocking layer is positioned over a portion of the capsule compositionand esterase when the capsule composition and esterase are placed in alocation where the presence of alpha particle radiation is beingdetermined. The operator should then compare the presence or extent ofleakage of the indicator solution from capsules in regions covered bythe alpha radiation blocking layer and regions not covered by the alpharadiation blocking layer to determine if regions not covered by thealpha radiation blocking layer exhibit leakage or a higher leakage ofthe solution compared to regions covered by the alpha radiation blockinglayer. If no (or less) leakage is observed in the capsule compositioncovered by the alpha radiation blocking layer compared to the capsulecomposition not covered by the alpha radiation blocking layer, theoperator has further evidence that alpha radiation is present. The alpharadiation blocking material can be any material well known in the arthaving a propensity for at least partially blocking alpha particleradiation, e.g., a sheet, strip, or other shape of paper, plastic, ormetallic foil.

The visual or olfactory indicator, once leaked, can be observed by anysuitable means. In the case of a fluorophore visual indicator, thefluorophore is typically stimulated with electromagnetic radiation(e.g., by laser light) to result in emission of light that can beobserved directly by the eye or through glasses or other device having awavelength filter. In the case of an olfactory indicator, the leakedscent may be observed directly by a human operator, or indirectly by useof an olfactory-acute animal (e.g., sniff dog) or artificial olfactorydevice.

In some embodiments, the detection method described above isspecifically directed to the detection of radon. The presence of radonmay be determined by any of the methods described above. However, asradon shares the unusual characteristic of being a gaseous alpharadiation emitter, the above described methods can be more specificallytailored for radon testing. In one set of embodiments, the method forradon testing includes, before step (i), placing an absorbent materialthat absorbs radon yet does not block alpha particle emission in alocation where the presence of radon is being determined. The absorbentmaterial can be, for example, a cryptophane material or a modified orrelated form thereof, wherein cryptophanes and derivatives thereof areknown in the art to be particularly adept in absorbing radon (e.g., D.R. Jacobson et al., Proc Natl Acad Sci USA. 2011 Jul. 5; 108(27):10969-10973; L. Laureano-Perez et al., Applied Radiation and Isotopes,70(9), pp. 1997-2001, September 2012; and K. T. Holman, “Cryptophanes:Molecular Containers”, in Atwood, J. L.; Steed, J. W. (eds.).Encyclopedia of Supramolecular Chemistry. CRC Press, 2004. pp. 340-348.doi:10.1081/E-ESMC. ISBN 0-8247-4723-2). In some embodiments, thecryptophane is more specifically Cryptophane A. Other radon absorbantsinclude bisphenol-A based polycarbonates, activated charcoal, andvarious oils including olive oil, and other vegetable oils. After theabsorbent material is provided sufficient time to absorb radon (e.g., atleast 1, 2, 3, or 4 days), the capsule composition and esterase areplaced in contact with each other on the absorbent material inaccordance with step (i). Subsequently, the capsule composition ismonitored for leakage over a period of time, as discussed above, inaccordance with steps (ii) and (iii), to determine the presence ofradon.

In further embodiments of the above radon detection method, the methodmay further involve, before step (i), placing the radon-absorbing(absorbent) material on selective portions of a substrate to result inregions of the substrate containing (coated with) the absorbent materialand regions of the substrate not containing (not coated with) theabsorbent material. The substrate, whose surface is selectively coatedwith the absorbent material, is then placed in a location where thepresence of radon is being determined. After the absorbent material isprovided sufficient time to absorb radon, the capsule composition andesterase are placed in contact with each other on regions containing theabsorbent material and regions not containing the absorbent material, inaccordance with step (i). Subsequently, the capsule composition ismonitored for leakage over a period of time, as discussed above, inaccordance with steps (ii) and (iii), to determine the presence ofradon. In the foregoing embodiment, step (iii) more particularlyincludes determining the presence or extent of leakage of the solutionin regions containing the absorbent material and comparing this resultto regions not containing the absorbent material to determine if regionscontaining the absorbent material exhibit leakage (or a higher leakage)of the indicator solution from the capsules compared to regions notcontaining the absorbent material.

Examples have been set forth below for the purpose of illustration andto describe certain specific embodiments of the invention. However, thescope of this invention is not to be in any way limited by the examplesset forth herein.

Examples

Method and Apparatus for Determining the Location of AlphaParticle-Generating Radioactive Contamination

Disclosed is a method and apparatus for determining the location ofalpha particle-generating radioactive contamination. Track etchrecording polymeric micro- and/or nano-capsules are filled with anindicator material and co-deposited with materials which etch or degradethe polymeric shell and for which this etching and degradation isdependent and/or sensitized and enhanced by the damage tracks impartedto the polymer by exposure to alpha particle radiation. Capsuledegradation by the combined influence of the etchant and alpha-particleradiation results in leakage of the capsule contents which may bemeasured by various methods to quantitatively determine the preciselocation of alpha-emitting radioactive contaminants upon surfaces uponwhich the etchant and nanocapsules have been colocalized.

A preferred embodiment of the capsules are fluorescent dye-containingnanocapsules produced via a dual emulsion technique whereby 25milligrams of poly(lactic-co-glycolic) acid (PLGA) are dissolved in 1milliliter of ethyl acetate and homogenized with an ultrasonic horn with50 microliters of 10 mM sodium fluorescein in water. The resultantemulsion is then vortexed into 2 milliliters of a solution of 0.3%D-alpha-tocopherol polyethylene glycol in water, followed by ultrasonichomogenization. This emulsion is then vortexed into 50 mL of the 0.3%E-TPGS solution, resulting in hardening of the PLGA capsules andformation of core shell particles of sodium fluorescein within PLGA.

Polymeric capsules are colocalized with an etchant and factors promotingthe degradation of the nanocapsules by the etchant. A preferredembodiment is to colocalize the polymeric capsules with lipase derivedfrom Rhizopus oryzae, pH buffer salts, and the surfactant Tween® 20which slowly degrades the polymeric capsules over time even under dryconditions. This degradation is significantly enhanced by exposure ofthe polymeric capsules to alpha particle radiation. FIG. 1 is a graphshowing the amount of leakage of fluorescein dye from PLGA nanocapsulesdeposited onto Durx® 770 polyester/cellulose clean room wipes andexposed to lipase over extended periods of time.

A preferred embodiment for colocalization of the polymeric capsules andthe etchants is aerosol dispersal of these materials using, for example,an aerosol fogging approach similar to insect ‘bombs’ used for dispersalof insecticides within interior enclosures. Polymeric capsules andetchant materials are initially stored in separate compartments andmixed upon activation of the aerosol dispersal device, generating anaerosol fog in which individual aerosol particles contain both thepolymeric capsules and the etchant mix, thereby allowing these materialsto colocalize upon surfaces within the fogged enclosure.

Colocalization of the polymeric capsules and etchant materials may alsobe performed by spraying the individual or mixed components uponsurfaces including walls, floors, tabletops, and upon materials that maybe wiped upon these surfaces such as cloths, sampling swabs, and uponother materials such as clothing, shoe soles, carpets, floor coverings,enclosure housings such as tents. Colocalization may also be achieved bycontaining both the indicator dye and the etchant mixture (for example,enzyme, buffer, and surfactant) within the capsules, provided there is asignificant difference in the etch rate of the polymer with and withoutalpha radiation exposure.

Polymeric capsule degradation, facilitated by alpha particle exposure,may be quantified and localized via various methods. A preferredembodiment is to contain a fluorescent dye within the capsule and toobserve leakage of the dye due to capsule degradation via fluorescentimaging systems which may include laser illuminators and appropriatelyfiltered laser safety goggles, illuminators and cameras with appropriatewavelength filtering. Dyes may also be non-fluorescent and colorimetricfor ambient light visualization or reactive for detection using anindicator reagent. Capsules may also contain other materials that may bedetected by other measurement modalities, including scents to whichcanines are trained or other odorants. A preferred embodiment is to fillcapsules with sodium fluorescein and to observe capsule degradation viause of a 520 nm laser diode flashlight, and Thorlabs LG3 laser safetygoggles with 545 nm high pass emission filtering.

FIG. 2 presents an optical image of a clean room wipe (Durx® 770) whichhas been pretreated with nanocapsules containing fluorescein andRhizopus oryzae lipase with phosphate buffer salts and Tween® 20, whichhas degraded the capsules over time while the wipe was maintained in adry, laboratory environment. The materials were deposited upon the wipeas 2 microliter spots as capsules alone, capsules with degradativeenzyme, enzyme alone, and blanks (no capsules nor enzymes). Thecapsule/enzyme combination resulted in degradation of the capsules andleakage of the internal fluorescein dye, visualized by 520 nm laserdiode excitation and filtering with LG3 laser safety goggles.

A preferred embodiment is to simultaneously disperse a variety ofcapsules filled with fluorophores with unique and separateexcitation/emission characteristics such that capsule degradation willbe observable at multiple wavelengths and thereby easy to discriminateagainst other fluorescent materials within the search vicinity. Thedegradation of polymeric capsules is dependent upon alpha-particleexposure and is specifically dependent upon alpha particles impingingupon and traveling through the polymeric shell and inducing a damagetrack through the material which subsequently enables or enhances thedegradation of that material along that damage track by the etchant. Aclassic example is alpha track etch recording whereby alpha particletracks within polycarbonate may be etched by a strong base. Similarly,the preferred embodiment of PLGA may be sensitized to enzymatic etchingby exposure of the PLGA capsules to alpha particle radiation. Otherpolymeric materials may also be used, and various polymer/enzymecombinations employed. FIG. 3 presents the amount of fluorescein leakedfrom PLGA nanocapsules co-immobilized onto Durx® clean room wipes withlipase enzyme and following exposure of those capsules to various dosesof alpha particle radiation from an Am-241 source. The alpha particleexposure sensitized the PLGA nanocapsules to degradation and facilitatedleakage of fluorescein from the capsules.

The system is useful for determining the precise location ofalpha-particle emitting radioactive contamination. Isotopic alphaparticles travel several centimeters in air and are stopped by materialsbased upon the interactions of the alpha particle and the material. Assuch, deposition of the capsule/etchant materials upon surfaces willaccurately reveal alpha contamination within several centimeters and theamount of indicator released from the system will be dose dependent.

The system is useful for alpha-particle emitting contaminant includingbut not limited to the following principle radioactive materials: 209Bi,211Bi, 212Bi, 213Bi, 210Po, 211Po, 212Po, 214Po, 215Po, 216Po, 218Po,215At, 217At, 218At, 218Rn, 219Rn, 220Rn, 222Rn, 226Rn, 221Fr, 223Ra,224Ra, 226Ra, 225Ac, 227Ac, 227Th, 228Th, 229Th, 230Th, 232Th, 231 Pa,233U, 234U, 235U, 236U, 238U, 237Np, 238Pu, 239Pu, 240Pu, 244Pu, 241Am,244Cm, 245Cm, 248Cm, 249Cf, and 252Cf.

A preferred embodiment to implement the above-described system is todeploy an aerosol bomb in a room in which alpha contamination issuspected and to close access to the room for 12 or more hours.Following this interval, the room is inspected by scanning the room witha laser flashlight and appropriately filtered laser safety glasses, orby implementing a LIDAR device to spatially map the room and denoteareas where the unique fluorescent signatures of the capsule system areindicated. This will permit decontamination crews to plan theirdecontamination operations to safety and effectively remove or seal theprecise sources of alpha emitting radioactive contaminants.

Another preferred embodiment is to co-localize dye containing capsulesand etchant materials onto solid materials (such as fabrics andcoverings) and to lay these materials upon a surface for extendedperiods of time such that alpha emitting contaminants upon that surfacewill irradiate the overlaying capsule-bearing cover. This approacheliminates the need for aerosol dispersal and may be preferred in somescenarios.

Another preferred embodiment is for radon detection. Small strips ofpaper are surface treated with nanocapsules containing a colorimetricdry and an appropriate chemical or enzymatic etchant, as describedabove. These detectors are then placed in areas to monitor for thepresence of alpha emitting radon gas within the environment overextended time periods (i.e. months). Preferred areas are low-lying areaswith minimal air exchange where dense radon gas might collect. Radonexposure will result in alpha irradiation of the capsules, therebypromoting their rupture and release of dye over extended time periods.As a positive control, a pre-irradiated region on the test strip(pre-irradiated with a known dose of alpha radiation) can be used as anindicator that the colorimetric test strip remains functional.

Such test strips can be inexpensively manufactured by spotting orprinting the capsules onto small regions of paper, and to use anadhesive backing on the paper (similar to post-it notes) to affix theindicators to surfaces of interest. The indicators can be read on aperiodic basis by looking for the colorimetric indication of capsulerupture which is dependent upon alpha exposure. Such indicators could becombined with other radon gas measurement modalities (such as charcoaltraps, which must be laboratory analyzed after a specific collectionperiod has elapsed), or ionization chambers which are expensive singlepoint analysis systems.

PLGA Capsule Production

PLGA capsules were produced using a double emulsion method. 25 mg ofPLGA (Resomer RG503:comprised of acid-terminated, lactide:glycolide50:50, MW 24000-38000) or (Lactel B6010-2:comprised of ester terminated,lactide:glycolide 50:50, MW 30000-60000) was dissolved in 1 mL of ethylacetate in a 13 mm×100 mm glass test tube. 2 microliters of 100 mMsodium fluorescein (dissolved in water) was added to the dissolvedpolymer solution and placed onto wet ice while homogenized for 10seconds with a 700 W ultrasonic homogenizer set at 40% amplitude. Theresultant emulsion was then added dropwise using a glass Pasteur pipetteto 2 mL of 0.3% tocopherol polyethylene glycol succinate (in water)while vortexing the solution within a 13 mm×100 mm glass test tube on alaboratory vortexer. The resultant emulsion was then placed on ice andultrasonicated for 3 cycles of 10-secs/10-sec rest. The resultantemulsion was then decanted into 45 mL of 0.3% weight/volume tocopherolpolyethylene glycol succinate stirred at 360 rpm. The mixture wasstirred overnight to allow hardening of the PLGA capsules via loss ofethyl acetate from the polymer emulsion into the aqueous solution. Othervariations of capsules were produced by altering the volume orconcentration of sodium fluorescein added to the PLGA-ethyl acetatesolution, or by using other fluorophores or other additives to theencapsulated solutions such as mineral oil and surfactants.

PLGA capsules were collected by centrifuging the mixture for 15 minutesat 17000 g in a fixed-angle ultracentrifuge. The supernatant wasdecanted and the capsules were re-suspended in 50 mL of water chilled to4° C. This procedure was repeated twice to result in PLGA capsulessuspended in water, with the final volume of added water being 4 mL.PLGA capsules in aqueous suspension were stored at 4° C.

Total Dye Loading of PLGA Capsules

Total dye loading of capsules was determined by saponification. PLGAcapsules were re-suspended into 10 mM potassium phosphate buffer (pH8.0) with 0.05% Tween® 20 or 1M potassium hydroxide by microcentrifuging100 μL of the capsules at 10000 g for 2 minutes, aspirating thesupernatant, and re-suspending the capsules in 100 μL of the respectivesolution. Fluorescence of the solution was assayed on a Perkin Elmer HTS7000 plate reader using a filter set for fluorescein (485 nmexcitation/520 nm emission) and a gain of 55. FIG. 4 summarizes thefluorescence emission of variously formulated capsules that continue tocontain their encapsulated dye (by suspension within potassium phosphatebuffer and Tween) vs. those that released their dye due tosaponification with potassium hydroxide.

Immobilization of PLGA Capsules on Surfaces

PLGA capsules were re-suspended into 10 mM potassium phosphate buffer(pH 8.0) with 0.05% Tween® 20 by microcentrifuging 100 μL of thecapsules at 10000 g for 2 minutes, aspirating the supernatant, andre-suspending the capsules in 100 μL of the buffer/surfactant solution.A modified 96-well plate was prepared by removing the plate bottom andaffixing a sheet of Durx® 770 clean room wipe to the plate to serve as aplate bottom. Capsule suspension was dispensed in 1-2 microliter volumesonto the Durx® 770 clean room wipes at fixed well locations, and allowedto dry.

Evaluation of Stability of PLGA Capsules to Solvent Exposure

The fixed well locations were subsequently and iteratively rewetted withethanol, methanol, and potassium hydroxide to evaluate the stability ofthe capsule to ethanol and methanol solvents. Fluorescence of thecapsules at fixed well locations were assayed on a Perkin Elmer HTS 7000plate reader using a filter set for fluorescein (485 nm excitation/520nm emission). FIG. 5 summarizes the fluorescence emission of PLGAcapsules after initial drying, after iterative wetting with ethanol andmethanol, and after saponification and dye release by exposure to 1Mpotassium hydroxide.

Evaluation of Enzymatic Degradation of Capsules

50 microliters of PLGA capsules were re-suspended into 10 mM potassiumphosphate buffer (pH 8.0) with 0.05% Tween® 20 and 2 μL was spotted intoeach of 24 microwells on a plate. Lipase derived from Rhizopus oryzaewas formulated at 1 mg in 10 μL of 10 mM potassium phosphate (pH 8.0)with 0.05% Tween® 20. 2 μL of this was added to spots on 2 wells, thendiluted 1:10 and this added to capsule spots in two wells, serially downto 20 ng per reaction. Each of the enzyme dilutions was also placed inhot (90° C.+) water for 10 minutes and this was also spotted toco-localize with PLGA capsules.

Fluorescence of the capsules at fixed well locations were assayed on aPerkin Elmer HTS 7000 plate reader after a period of 19 days using afilter set for fluorescein (485 nm excitation/520 nm emission).Periodically, the spots were rewetted briefly (minutes) to promoteleakage of the dry fluorescein within the capsules. The results areprovided in FIG. 6. Increasing enzyme concentration resulted in higheramounts of fluorescence due to dye leakage. Heat denatured enzyme, evenat the highest concentrations of enzyme used, resulted in substantiallyless fluorescence due to leakage.

Evaluation of Alpha-Induced Enzymatic Degradation of Capsules

PLGA capsules were re-suspended into 10 mM potassium phosphate buffer(pH 8.0) with 0.05% Tween® 20 and 50 micrograms of lipase from Rhizopusoryzae. 2 μL aliquots were spotted into individual wells of a 96-wellplate with the bottom removed and replaced by a sheet of Durx® 770 cleanroom wipe. Spots were allowed to dry and irradiated for various times(120 min, 60 min, 15 min, 10 min, 5 min, 2 min) with a 0.9 microcurieAmericium-241 alpha source where the alpha source was located 1 cm aboveeach spot. The spots were rewetted with 2 microliters of water at 72 hrsand the fluorescence was measured using a Perkin Elmer HTS 7000 platereader with fluorescein filter set. Alpha exposure resulted in increasedfluorescence from the capsule spots (n=6 samples) vs. capsules that werenot irradiated (n=6) due to enhanced degradation of the capsule, asshown in FIG. 3.

Improved Sensitivity to Alpha-Induced Degradation of Capsules

PLGA capsules produced using either Resomer RG503 or Lactel B6010-2 PLGAwere re-suspended into 10 mM potassium phosphate buffer (pH 8.0) with0.05% Tween® 20 with and without 1/20 Unit of lipase from Rhizopusoryzae. 2 μL aliquots of each PLGA type (Resomer or Lactel) were spottedinto 12 individual wells of a 96-well plate (6 with enzyme, E+ and 6without enzyme E−) with the bottom removed and replaced by a sheet ofDurx® 770 clean room wipe. Spots were allowed to dry and half of eachPLGA type was irradiated for 2 minutes with a 0.9 microcurieAmericium-241 alpha source where the alpha source was located 1 cm aboveeach spot (E−I+=no enzyme irradiated; E+I+=enzyme and irradiated). Thespots were rewetted with 2 microliters of water at 72 hrs and thefluorescence was measured using a Perkin Elmer HTS 7000 plate readerwith fluorescein filter set. As shown in FIGS. 7A and 7B, while theResomer microcapsules (FIG. 7A) resulted in significant fluorescence dueto enzyme etching alone, the Lactel PLGA capsules (FIG. 7B) presented alarger irradiation induced leakage compared to unirradiated enzymaticdegradation of the capsules compared against the Resomer PLGAformulation. This permits greater sensitivity to alpha particleradiation and may increase the length of time that microcapsule andenzymes can be colocalized before resulting in leakage due to enzymeactivity alone without alpha exposure.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, those skilled in the art maymake various changes and modifications which remain within the scope ofthe invention defined by the appended claims.

What is claimed is:
 1. A capsule composition comprising: (a) a polyestershell having a thickness of no more than 20 microns, and (b) a solutioncontaining a visual indicator, wherein said solution is encapsulated bysaid polyester shell.
 2. The capsule composition of claim 1, whereinsaid polyester is a polyhydroxyalkanoate having the following structure:

wherein R¹ is selected from a hydrogen atom or hydrocarbon group, t isan integer from 0 to 4, n is an integer of at least 10, and saidstructure can be a homopolymer or copolymer.
 3. The capsule compositionof claim 2, wherein said polyhydroxyalkanoate is selected from the groupconsisting of polylactic acid, polyglycolic acid,poly(3-hydroxypropionic acid), poly(hydroxybutyric acid)s,poly(hydroxyvaleric acid)s, poly(hydroxyhexanoic acid)s,polycaprolactone, polymandelic acid, and copolymers thereof.
 4. Thecapsule composition of claim 2, wherein said polyhydroxyalkanoatecomprises polylactic acid, polyglycolic acid, or copolymer thereof. 5.The capsule composition of claim 2, wherein said polyhydroxyalkanoatecomprises a copolymer of lactic acid and glycolic acid.
 6. The capsulecomposition of claim 5, wherein said lactic acid and glycolic acid unitsin said copolymer are independently present in a molar amount of 40-60%,wherein the molar amounts of lactic acid and glycolic acid units sum to100%.
 7. The capsule composition of claim 1, wherein said polyester hasa number-average or weight-average molecular weight of at least 20,000g/mol.
 8. The capsule composition of claim 1, wherein said polyester hasa number-average or weight-average molecular weight of at least 30,000g/mol.
 9. The capsule composition of claim 1, wherein said polyester hasa number-average or weight-average molecular weight of at least 40,000g/mol.
 10. The capsule composition of claim 1, wherein said polyester isacid-terminated.
 11. The capsule composition of claim 1, wherein saidpolyester is ester-terminated.
 12. The capsule composition of claim 1,wherein said visual indicator is a fluorophore.
 13. The capsulecomposition of claim 1, wherein said visual indicator is anon-fluorophore dye.
 14. A method for detecting alpha particleradiation, the method comprising: (i) placing a capsule composition andesterase in contact with each other in a location where the presence ofalpha particle radiation is being determined, wherein said capsulecomposition comprises: (a) polyester shells having a thickness of nomore than 20 microns, and (b) a solution containing a visual orolfactory indicator, wherein said solution is encapsulated by saidpolyester shells; (ii) waiting a period of time for the esterase todegrade the polyester shells, wherein said period of time isinsufficient for the esterase to cause leakage of the solution from thecapsule composition in the absence of alpha particle radiation, whilesaid period of time is sufficient for alpha particle radiation, ifpresent, to degrade the polyester shells to the extent that leakage fromthe capsule composition would occur; and (iii) observing whether leakagefrom the capsule composition occurs at the completion of said period oftime to determine whether alpha particle radiation is present.
 15. Themethod of claim 14, wherein, in step (iii), if alpha particle radiationis determined to be present, the magnitude of alpha particle radiationis also determined by observing the degree of capsule leakage.
 16. Themethod of claim 15, wherein said polyester is a polyhydroxyalkanoatehaving the following structure:

wherein R¹ is selected from a hydrogen atom or hydrocarbon group, t isan integer from 0 to 4, n is an integer of at least 10, and saidstructure can be a homopolymer or copolymer.
 17. The method of claim 16,wherein said polyhydroxyalkanoate is selected from the group consistingof polylactic acid, polyglycolic acid, poly(3-hydroxypropionic acid),poly(hydroxybutyric acid)s, poly(hydroxyvaleric acid)s,poly(hydroxyhexanoic acid)s, polycaprolactone, polymandelic acid, andcopolymers thereof.
 18. The method of claim 16, wherein saidpolyhydroxyalkanoate comprises polylactic acid, polyglycolic acid, orcopolymer thereof.
 19. The method of claim 16, wherein saidpolyhydroxyalkanoate comprises a copolymer of lactic acid and glycolicacid.
 20. The method of claim 14, wherein said esterase is a lipase. 21.The method of claim 14, wherein the alpha emitting particles compriseradon.
 22. The method of claim 21, wherein, before step (i), the methodfurther comprises placing an absorbent material that absorbs radon yetdoes not block alpha particle emission in a location where the presenceof radon is being determined, and, in step (i), placing the capsulecomposition and esterase in contact with each other on said absorbentmaterial after the absorbent material is provided sufficient time toabsorb radon.
 23. The method of claim 21, wherein, before step (i), themethod further comprises placing an absorbent material that absorbsradon yet does not block alpha particle emission on selective portionsof a substrate to result in regions of the substrate containing theabsorbent material and regions of the substrate not containing theabsorbent material, and placing the substrate in a location where thepresence of radon is being determined, and, in step (i), placing thecapsule composition and esterase in contact with each other on saidregions containing the absorbent material and said regions notcontaining the absorbent material after the absorbent material isprovided sufficient time to absorb radon; proceeding with steps (ii);and in step (iii), determining the presence or extent of leakage of thesolution in regions containing the absorbent material and comparing thisresult to regions not containing the absorbent material to determine ifregions containing the absorbent material exhibit leakage or a higherleakage of the solution compared to regions not containing the absorbentmaterial.
 24. The method of claim 22, wherein said absorbent materialcomprises a cryptophane.
 25. The method of claim 14, wherein, in step(i), said capsule composition and esterase are present on a sheetsubstrate material when placed in a location where the presence of alphaparticle radiation is being determined.
 26. The method of claim 25,wherein an alpha radiation blocking layer is positioned over a portionof the capsule composition and esterase when said sheet substratematerial coated with the capsule composition and esterase is placed in alocation where the presence of alpha particle radiation is beingdetermined, and comparing the presence or extent of leakage of thesolution in regions covered by said alpha radiation blocking layer andregions not covered by said alpha radiation blocking layer to determineif regions not covered by said alpha radiation blocking layer exhibitleakage or a higher leakage of the solution compared to regions coveredby said alpha radiation blocking layer.